Tuning indicator tube



P 1933- H. c. THOMPSON 2,130,162

TUNING INDICATOR TUBE Original Filed June 27, 1935 INVENTOR HARRY C.THOMPSON ama Patented Sept. 13, 1938 UNITED STATES PATENT OFFICE TUNINGINDICATOR TUBE tion of Delaware Original application June 27, 1935,Serial No. 28,665. Divided and this application May 19,

1936, Serial No. 80,474

4 Claims.

My invention relates to electron discharge devices, more particularly tosuch devices useful as visual indicators of voltage and having afluorescent electrode which is rendered luminous, and has the appearanceof a pattern of light which may be of constant height or length andvarying width and which changes in response to the change in themagnitude of the applied voltage, a device of this character beingparticularly useful as a tuning indicator in radio receiving sets.

This application is a division of application No. 28,665, now Patent No.2,051,188, issued August 8, 1936, filed June 27, 1935 and assigned tothe same assignee as the present application.

It is an object of my invention to provide an improved electrondischarge device of the kind described, which is particularly suitablefor use as a visual tuning indicator in a radio receiving set and inwhich resonance is indicated by a brilliant luminous glow on anelectrode.

In general my invention comprises an envelope having within it astraight thermionic cathode having two separate electron emittingsections around one of which are positioned at least one grid and ananode. Around the other section are mounted the visual tuning indicatorelements comprising preferably a straight control electrode parallel tothe cathode, and an anode which may be flat or cylindrical and may be ofsheet or of mesh material and coated with material which fluoresces inresponse to electron bombardment. In operation the electrons flow fromthe cathode to the anode with suflicient, velocity to bombard the plateand render it luminous. The control electrode is electrically connectedto the anode surrounding the grid and the elements of the tube are soconnected in a radio receiving circuit that when the circuit is tuned toresonance with an incoming signal the luminous portion of the indicatoranode is of a predetermined size. In one form of the device theconnection is such that the luminous portion of the anode is of a maXimum width and hence the dark space of minimum width when the circuit istuned to reso nance, the height or length remaining constant.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims, but theinvention itself will best be understood by reference to the followingdescription taken in connection with the accompanying drawing in whichFigure 1 shows an electron discharge device embodying my invention withparts broken away to show details of construction; Figure 2 is anenlarged top and side view showing details of construction of thevoltage indicating elements of the tube shown in Figure 1; Figure 3shows a circuit arrangement using a tube made in accordance with myinvention; and Figures 4 and 5 are top views of further modifications ofthe tuning indicator elements of the electron discharge device shown inFigure l.

The electron discharge device or tuning indicator tube shown in Figure 1comprises an evacuated envelope l provided with the usual stem and pressII, and base I 2. Supported from the press are a cathode l3, preferablythe conventional indirectly heated equipotential type, a grid l4 andanode l surrounding the cathode.

In accordance with my invention I mount in the dome portion of theenvelope Ill the visual indicating portion of the tube comprising acathode, a control electrode and an anode having preferably a fiatsurface presented to said cathode and control electrode and providedwith a coating which fiuoresces when subjected to electron bombardment.While the anode having the fiuorescent coating may be of the mesh typeand viewed from either side and might have fiat or curved surfaces, Imay make it of fiat or curved sheet material and coat only one side,which may be directly viewed.

As shown in Figures 1 and 2 the cathode I3 is extended into the domeportion of the envelope as shown at I6 and has a second emitting section16' for applying the electrons in the visual indicating device. Acontrol electrode 25 in the form of a cylinder provided with alongitudinal opening 26 through which electrons pass from the cathodeemitting portion Hi to the flat coated anode 21 surrounds the cathodeand is supported from a cross bar [8 electrically connected to the siderods 19 of the anode !5. This control electrode determines the patternof the luminescent portion of the anode Zl, which is shown as made ofsheet material and coated with any conventional luminescent material,and is supported by rods 2! extending from the press II.

In operation the voltage on the anode I5 is applied to the controlelectrode 25, the voltage on this electrode determining the width of thepattern of light on the anode 21, the height of the pattern of lightbeing constant and equal to the height of the anode. The less negativethis control electrode 25 is biased with respect to the anode 2'? thewider will be the luminescent area (b) on the anode 21 inasmuch as thebeam of electrons from the cathode becomes less sharply focused thanwhen the negative bias on the control electrode is large and theluminescent area (a) is narrower. In this embodiment of my invention theluminescent portion of the voltage or tuning indicator may be viewedfrom the side of the tube with ease. The emitting area l6 of the cathodeI6 is confined as shown to prevent the control electrode 25 drawinganysubstantial amount of current.

Referring to Figure 2, which shows a top view of the tuning indicatorportion of the invention shown in Figure 1, the beam control electrode25 is so biased that when no signal is being received the voltagedifference between the control electrode 25 and the anode 21 is suchthat only the portion a of the anode is luminescent. As the set is tunedto resonance the voltage difference between the anode 21 and theelectrode 25 becomes less, so that the control effect of the electrode25 on the electrons leaving the cathode I6 is less, permitting electronsfrom the cathode IE to reach more of the anode 21 so that when the setis tuned to resonance the anode is luminous over the surface as shown bylines I).

The application of an electron discharge de vice made in accordance withmy invention to a radio circuit is shown in Figure 3. Normally the anode15 of the triode section of the tube is electrically connected through aresistor 49, to a source of voltage 4|. The indicator anode is connecteddirectly to the source of voltage 4|. With no voltage on the grid 14 acertain predetermined amount of current flow through the triode sectionof the tube causes a drop in resistor 40, so that the Voltages appliedto anode l5 and indicator anode 21 have the greatest differential, thevoltage on anode l5 being at the lower potential. The voltage on anode21 does not change While that on the anode [5 decreases, due to the dropthrough resistor 40. This makes the control electrode 25 negative withrespect to anode 21, thus reducing the width of the luminescent portionof the anode 21. As the voltage on the control grid 14 increases in thenegative direction the current flow to the anode l5 decreases so thatthe voltage drop through the resistor 40 decreases. Under thesecircumstances the voltage differential between anode l5 and indicatinganode 21 decreases: so that the control electrode 25 becomes lessnegative with respect to the anode 21. This permits the width of theluminescent portion to increase. Thus the luminescent portion increasesas the negative bias on the control grid l3 increases. Thischaracteristic of the tuning indicator tube is made use of whenconnected to a conventional automatic volume control circuit. Therectifier tube 42 has an anode 43 connected to one side of the radiofrequency or intermediate frequency transformer 44 coupled to thereceiving circuit not shown, and a cathode 45 connected through a gridleak 46 and by-pass condenser 41 to the other side of the transformer44. The cathode side of the transformer 44 is connected through resistor48 to control grid 1 4 of the tuning indicator tube. A radio frequencyby-passing condenser 49 connects the grid to ground, and the conductor50 may be connected to other parts of the circuit to provide automaticvolume control. As the receiving circuit is tuned to resonance andrectification takesplace through the tube 42, the cathode side of theradio frequency transformer becomes negative with respect to ground dueto the current through resistor 46. This negative voltage is applied tothe control grid 14 as a negative bias with the result that the currentthrough the triode portion of the tube is reduced, thus causing thewidth of the luminescent portion of the tuning indicator anode 21 toincrease as explained above. In this arrangement the control electrodeis positive with respect to the cathode. Several advantages follow fromthis arrangement over that in which the control electrode is biasednegatively with respect to the cathode. The boundaries of the electronbeams are sharp and well defined. There can be a high concentration ofelectrons at the edges of the luminous areas so that the luminosity isuniform. The high current to the luminescent portion of the screen canbe obtained at low voltages and hence a high luminosity is the result. Apositive control electrode is suitable for direct coupling to anamplifier, that is it may be directly connected to the plate of anamplifier tube as shown in Figure 1 for example. Furthermore, a tubemade in accordance with my invention is not critical to variations incathode temperatures and is susceptible for use with alternating anddirect voltages and current:

In Figure 4 the control electrode 30 is a V- shaped member on one sideof the electron emitting cathode l6 and the luminescent anode issimilarly shaped with the coating on the side facing the cathode. Figure5 shows an arrangement very similar to that shown in Figure 4 exceptthat the control electrodes 35 and anode 36 are flat.

In the embodiment shown in Figures 4 and 5 the control electrodes 30 and35 may be connected to the grid of the triode section, so that they arebiased negatively with respect to the cathode. With this connection theluminescent portions between the lines a and b in Figures 4 and 5indicate the luminescent portions when the circuit in which the tube isused is tuned and untuned to an incoming signal.

While I have indicated the preferred embodiment of my invention of whichI am now aware and have also indicated only one specific application forwhich my invention may be employed, it will be apparent that myinvention is by no means limited to the exact forms illustrated or theuse indicated, but that many variations may be made in the particularstructure used and the purpose for which it is employed withoutdeparting-from the scope of my invention as set forth in the appendedclaims.

What I claim as new is:

1. An electron discharge device having an envelope enclosing a straightthermionic electron emitting cathode, an anode having a flat surfaceadjacent said cathode and having a fluorescent coating thereon, acontrol electrode comprising a pair of straight conductors parallel toand on the opposite side of the cathode from said anode for determiningthe extent of the anode reached by the electrons emitted by the cathode.

2. An electron discharge device having an envelope, a cathode within theenvelope having a plurality of electron emitting surfaces along itssurface, a grid and anode surrounding one of said electron emittingsurfaces and a fluorescent anode having a flat surface adjacent anotherof the electron emitting surfaces of said cathode and a, controlelectrode positioned on the opposite side of the cathode from saidfluorescent anode and comprising a conductor parallel to the cathode andconnected to the anode surrounding the grid for producing on saidfluorescent anode a beam of substantially constant length and of a widthdepending upon the voltage applied to said control electrode through theanode around the grid.

3. An electron discharge device having an envelope, a straightthermionic cathode within said envelope for emitting electrons, aV-shaped anode adjacent the cathode and coextensive therewith and coatedwith a material which fluoresces when struck by electrons from saidcathode and a control electrode comprising a V-shaped member on theother side of said cathode from said anode and coextensive with saidcathode and anode, the width of the luminescent portion of the anodestruck by said electrons being dependent on the voltage applied to saidcontrol electrode.

terial and electrically connected to and sup-port- 10 ed by the anodesurrounding said grid.

HARRY C. THOMPSON.

